One method of filling a volume with liquid involves the use of a pointed fill needle that is attached to a syringe containing the liquid to be injected, piercing a wall of the volume with the needle, and pumping the liquid from the syringe into the volume. In order to accommodate this method, the wall of the volume is fitted with a rubber or rubber-like fill area that can be pierced by the needle. Ideally, when the needle is removed after the fill step, the rubber closes around the puncture, sealing the opening. In order for the fill area to be leak free, the needle must be of a “non-coring” type. And also, the surface of the needle must be smooth in order to prevent tearing of the rubber that could provide a path for liquid to escape. Depending on the tear characteristics of the rubber, and its dimensions at the fill area, the fill needle may have to be relatively small, in many cases less than one millimeter in diameter, to avoid post-fill leakage.